1. Field of the Invention
The present invention relates to a semiconductor device, an imaging device, a method of inspecting a semiconductor substrate, and a method of fabricating a semiconductor device.
Priority is claimed on Japanese Patent Application No. 2012-234955, filed Oct. 24, 2012, the content of which is incorporated herein by reference.
2. Description of Related Art
In general, video cameras, electronic still cameras, and the like have been widely used. In these cameras, charge-coupled device (CCD) type or amplification type solid-state image sensors have been used. In the amplification type solid-state image sensors, signal charges generated and accumulated in a photoelectric converter of a light-receiving pixel are led to an amplification unit provided in the pixel. The amplification unit outputs an amplified signal from the pixel. In the amplification type solid-state image sensor, such a pixel is arranged in plural in a matrix form. As the amplification type solid-state image sensor, for example, there is a complementary metal oxide semiconductor (CMOS) type solid-state image sensor using a CMOS transistor.
In the related art, in a general CMOS type solid-state image sensor, a method of sequentially reading out signal charges generated and accumulated in a photoelectric converter of each pixel arranged in a two-dimensional (2D) matrix form in units of pixel rows is employed. At this time, since an exposure timing in the photoelectric converter of each pixel is determined in accordance with start and stop of read-out of the signal charges, the exposure timings for each pixel are different. Therefore, when a fast moving subject is imaged using the CMOS type solid-state image sensor, the subject is distorted and imaged.
To eliminate the distortion of the subject, a simultaneous imaging function (a global shutter function) which realizes simultaneity of accumulation of the signal charges is suggested. Further, the use of the CMOS type solid-state image sensor having the global shutter function is increasing. In the CMOS type solid-state image sensor having the global shutter function, conventionally, in order to accumulate the signal charges generated in the photoelectric converter until the signal charges are read out, it is necessary to have a storage capacitor having a light-shielding property. In such a CMOS type solid-state image sensor in the related art, after all the pixels are simultaneously exposed, the signal charges generated in the photoelectric converters of all the pixels are simultaneously transferred to the storage capacitors and first accumulated. The signal charges are sequentially converted into pixel signals at a predetermined read-out timing.
However, in the CMOS type solid-state image sensor having the global shutter function in the related art, the photoelectric converter and the storage capacitor have to be formed on the same plane of a substrate. Thus, in the CMOS type solid-state image sensor, a wafer area, which is an area which a solid-state image sensor occupies on a wafer in which the solid-state image sensor is formed, is inevitably increased. Further, during a stand-by period until the signal charges accumulated in the storage capacitor are read out, there is a problem that signal quality is deteriorated by noise due to leakage of light or storage capacitance.
To solve the problem, for example, in Japanese Patent Publication No. 4349232, a solid-state image sensor including a back-illuminated type MOS image sensor wafer and a signal-processing wafer mutually connected by a micro bump is disclosed. In the MOS image sensor wafer, a micro pad is formed in a wiring layer side every unit pixel. In the signal-processing wafer, a micro pad is formed in a wiring layer side at a location corresponding to the micro pad of the MOS image sensor wafer. Further, for example, in Japanese Unexamined Patent Application, First Publication No. 2010-219339, a method is disclosed for preventing an increase in a wafer area by a solid-state image sensor in which a first substrate formed with a photoelectric converter and a second substrate formed with a plurality of MOS transistors are bonded.
A process of inspecting an operation of each wafer is performed before the MOS image sensor wafer and the signal-processing wafer are connected by the micro bump (hereinafter, referred to as a bump) and the like. Improvement in yield is promoted by fabricating the image sensor by connection of the wafers whose operation is to be checked in the inspection process. The inspection is performed by pressing a probe needle to an electrode formed on a wafer surface.